Inkjet recording apparatus

ABSTRACT

An inkjet recording apparatus includes three or more recording heads. The recording heads contain different inks and eject the different inks sequentially on a recording medium. The different inks each contain a pigment. Of the different inks, an ink to be ejected first has the lowest pigment content ratio. Of the different inks, an ink to be ejected third and an ink to be subsequently ejected each have a pigment content ratio equal to or higher than that of the pigment contained in a corresponding one of inks to be precedently ejected. Of the different inks, an ink to be ejected second and an ink to be subsequently ejected each have a lower viscosity at 25° C. than a corresponding one of inks to be precedently ejected.

INCORPORATION BY REFERENCE

The present application claims priority under 35 U.S.C. § 112 toJapanese Patent Application No. 2018-190020, filed on Oct. 5, 2018. Thecontents of this application are incorporated herein by reference intheir entirety.

BACKGROUND

The present disclosure relates to an inkjet recording apparatus.

Rapid progress on inkjet recording apparatuses has been made in recentyears to achieve image quality having high definition comparable withsilver halide photographs in a case using photographic paper. Examplesof printing processes adoptable to an inkjet recording apparatus includea recording process using a line type recording head and a recordingprocess using a serial type recording head. The recording process usinga line type recording head is a process in which a long recording headpasses over a recording medium only one time. The recording processusing a serial type recording head is a process in which a recordinghead reciprocates over a recording sheet plural times. An inkjetrecording apparatus that adopts the recording process using a line typerecording head among the printing processes is high in printing speed.

However, the inkjet recording apparatus adopting the recording processusing a line type recording head does not perform overlaying printingunlike an inkjet recording apparatus adopting the recording processusing a serial type recording head. Accordingly, image offset (aphenomenon in which an image adheres to a member of the inkjet recordingapparatus) tends to occur in high-speed printing by the inkjet recordingapparatus adopting the recording process using a line type recordinghead. Image offset by the inkjet recording apparatus adopting therecording process using a line type recording head is particularlysignificant when plural inks are used in combination for secondary ortertiary color drawing.

As a method for favorable image formation with plural inks using aninkjet recording apparatus adopting the recording process using a linetype recording head, methods have been proposed in which viscosity orpigment concentration of each ink is changed according to order ofejection. Specifically, examples of the propose methods include: amethod in which an ink to be ejected earlier in order of ejection hashigher pigment concentration; a method in which the viscosity of an inkto be ejected later in order of ejection is set lower by increasingejection temperature; and a method in which an ink to be ejected laterin order of ejection has higher viscosity.

SUMMARY

An inkjet recording apparatus according to an aspect of the presentdisclosure includes three or more recording heads. The recording headscontain respective different inks and eject the respective differentinks sequentially on a recording medium. The different inks each containa pigment. Of the different inks, an ink to be ejected first has alowest pigment content ratio. Of the different inks, an ink to beejected third and an ink to be subsequently ejected each have a pigmentcontent ratio equal to or higher than that of a corresponding one ofinks to be precedently ejected. Of the different inks, an ink to beejected second and an ink to be subsequently ejected each have a lowerviscosity at 25° C. than a corresponding one of inks to be precedentlyejected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a configuration of an inkjet recordingapparatus according to a first embodiment of the present disclosure.

FIG. 2 is a view of a conveyor belt of the inkjet recording apparatusillustrated in FIG. 1 as viewed from above.

FIG. 3 is a diagram illustrating an ejection unit of a recording headillustrated in FIG. 2.

FIG. 4 is a cross-sectional view taken along a line IV-IV in FIG. 3.

FIG. 5 is a block diagram illustrating the configuration of the inkjetrecording apparatus in FIG. 1.

DETAILED DESCRIPTION

The following describes embodiments of the present disclosure. In thefollowing description, measurement values for volume median diameter(D₅₀) are values measured using a dynamic light scattering type particlesize distribution analyzer (“ZERASIZER NANO ZS”, product of SysmexCorporation), unless otherwise stated. Measurement values for acid valueare values measured in accordance with “Japanese Industrial Standard(JIS) K0070-1992”, unless otherwise stated. Measurement values for massaverage molecular weight (Mw) are values measured by gel permeationchromatography, unless otherwise stated. Note that in the presentdescription, the term “(meth)acryl” is used as a generic term for bothacryl and methacryl.

First Embodiment: Inkjet Recording Apparatus

A first embodiment of the present disclosure relates to an inkjetrecording apparatus. The inkjet recording apparatus according to thepresent embodiment includes three or more recording heads. The recordingheads contain different inks and eject the different inks sequentiallyon a recording medium. The different inks each contain a pigment. Of thedifferent inks, an ink to be ejected first has the lowest pigmentcontent ratio. Of the different inks, an ink to be ejected third and anink to be subsequently ejected each have a pigment content ratio equalto or higher than that of the pigment contained in a corresponding oneof inks to be precedently ejected. Of the different inks, an ink to beejected second and an ink to be subsequently ejected each have a lowerviscosity at 25° C. than a corresponding one of inks to be precedentlyejected.

Examples of recording mediums that can be used in the inkjet recordingapparatus according to the present embodiment include recording mediumsmade from paper, resin, metal, glass, or ceramics. Either a permeablerecording medium or a non-permeable recording medium may be used, but apermeable recording medium is preferable. Specific examples of therecording medium include plain paper and coated paper made to bemoisture absorbable. Another example of recording mediums is a recordingmedium processed with fiber (for example, cloth). That is, the inkjetrecording apparatus according to the present embodiment can be used forinkjet textile printing.

In the following description, a recording head of all the recordingheads of the inkjet recording apparatus that ejects an ink the n-th maybe referred to as an n-th recording head (n is an integer of at least1). Also, an ink of all the inks that is to be ejected the n-th by then-th recording head of the inkjet recording apparatus may be referred toas an n-th ink (n is an integer of at least 1). For example, a recordinghead of all the recording heads that ejects an ink first is referred toas a first recording head. Also, an ink of all the inks that is to beejected first by the first recording head is referred to as a first ink.A recording head of all the recording heads that ejects an ink the lastis referred to as a last recording head. An ink of all the inks that isto be ejected the last by the last recording head may be referred to asa last ink.

The inkjet recording apparatus according to the present embodiment hasthe above configuration and can therefore prevent offset of a formedimage. Presumably, the reason therefor is as follows.

In sequential ejection of a plurality of inks to a recording medium, anink ejected relatively later tends to permeate less through therecording medium than an ink ejected relatively earlier. This is becausea portion of a pigment contained in an ink ejected onto the recordingmedium tends to remain on the surface of the recording medium withoutpermeating therethrough to inhibit permeation of an ink ejectedthereafter through the recording medium. The above phenomenon(phenomenon in which permeability of a later-ejected ink to a recordingmedium is impaired due to the presence of an earlier-ejected ink)readily occur with an increase in pigment content ratio in theearlier-ejected ink. In particular, the above phenomenon significantlyreadily occurs when the first ink to be ejected to a recording mediumfirst has a high pigment content ratio. By contrast, in the inkjetrecording apparatus according to the present embodiment, an ink having ahigher pigment content ratio is to be ejected later and an ink of allthe inks that has the lowest pigment content ratio is to be ejectedfirst. In the above configuration, the inkjet recording apparatusaccording to the present embodiment can significantly prevent the abovephenomenon.

In a case where the recording medium is made from a porous material (forexample, printing paper), permeability of an ink to the recording mediumis expressed by the following Lucas-Washburn equation. In the followingequation, L represents a permeation distance [m], r represents acapillary radius [m], γ represents a surface tension [mN/m], ηrepresents a viscosity [mPa·s] of an ink, θ represents a contact angle[°] between a recording medium and the ink, and t represents time [s]. Alarger permeation distance L indicates that the ink more readilypermeates through the recording medium. As is clear from the followingequation, an ink having a lower viscosity (η) more readily permeatesthrough the recording medium.

$L = \sqrt{\frac{r\;\gamma\mspace{11mu}\cos\mspace{11mu}\theta}{2\eta}t}$

In the inkjet recording apparatus according to the present embodiment,the ink to be ejected second and an ink to be subsequently ejected eachhave a lower viscosity than a corresponding one of inks to beprecedently ejected. That is, an ink to be ejected later has a lowerviscosity (or, an ink to be ejected later is excellent in permeabilityto the recording medium) in the inkjet recording apparatus according tothe present embodiment. In the above configuration in the inkjetrecording apparatus according to the present embodiment, even an ink tobe ejected to a recording medium relatively later in order cansufficiently permeate through the recording medium through adjustment asabove of the viscosity and the pigment content ratios of each inkaccording to the order of ejection to the recording medium, with aresult that offset of a formed image can be prevented.

The following describes the inkjet recording apparatus according to thepresent embodiment with reference to the drawings. The drawingsschematically illustrate elements of configuration in order tofacilitate understanding. The elements of configuration illustrated inthe drawings may differ from actual ones in properties such as size andthe number thereof in order to facilitate preparation of the drawings.

FIG. 1 is a diagram illustrating a configuration of an inkjet recordingapparatus 100. FIG. 2 is a view of a conveyor belt 5 of the inkjetrecording apparatus 100 illustrated in FIG. 1 as viewed from above.

As illustrated in FIG. 1, the inkjet recording apparatus 100 includes aconveyance section 1 and a recording head group 11 as main elements ofconfiguration. The inkjet recording apparatus 100 further includes asheet feed tray 2, a sheet feed roller 3, a sheet feed driven roller 4,a conveyor belt 5, a belt drive roller 6, a belt driven roller 7, anejection roller 8, an ejection driven roller 9, and an exit tray 10. Theconveyor belt 5, the belt drive roller 6, and the belt driven roller 7constitute part of the conveyance section 1. The sheet feed tray 2 isprovide at a left end of the inkjet recording apparatus 100 in thedrawing. Recording sheets P (recording mediums) are loaded on the sheetfeed tray 2. The sheet feed roller 3 and the sheet feed driven roller 4are disposed at an end of the sheet feed tray 2. The sheet feed roller 3picks up the loaded recording sheets P one at a time from a topmostrecording sheet P and feeds the recording sheet P to the conveyor belt 5for conveyance. The sheet feed driven roller 4 is in contact by pressurewith the sheet feed roller 3 to passively rotate.

The conveyor belt 5 is arranged downstream of the sheet feed roller 3and the sheet feed driven roller 4 (right side in FIG. 1) in terms of aconveyance direction X of the recording sheet P in a circulatablemanner. The conveyor belt 5 is wound between the belt drive roller 6 andthe belt driven roller 7. The belt drive roller 6 is disposed downstreamof the belt driven roller 7 in terms of the conveyance direction X ofthe recording sheet P. The belt drive roller 6 drives to circulate theconveyor belt 5. The belt driven roller 7 is disposed upstream of thebelt drive roller 6 in terms of the conveyance direction X of therecording sheet P. The belt driven roller 7 passively rotates withrotation of the belt drive roller 6 through the conveyor belt 5. Whenthe belt drive roller 6 drives and rotates clockwise in the drawing, therecording sheet P is conveyed in the conveyance direction X of therecording sheet P indicated by an arrow in FIG. 1.

The ejection roller 8 and the ejection driven roller 9 are disposeddownstream of the conveyor belt 5 in terms of the conveyance directionX. The ejection roller 8 is driven and rotated clockwise in the drawingto eject the recording sheet P with an image formed thereon out of anapparatus casing. The ejection driven roller 9 is in contact by pressurewith an upper part of the ejection roller 8 to passively rotate. Theexit tray 10 is disposed downstream of the ejection roller 8 and theejection driven roller 9 in terms of the conveyance direction X. Theexit tray 10 receives the recording sheet P ejected out of the apparatuscasing.

The recording head group 11 includes recording heads 11C, 11M, 11Y, and11K. The recording heads 11C, 11M, 11Y, and 11K are arranged above theconveyor belt 5 in the stated order from upstream to downstream in termsof the conveyance direction X of the recording sheet P. Each of therecording heads 11C to 11K is supported at a level a specific distanceapart from an upper surface of the conveyor belt 5. The recording heads11C to 11K each record an image on the recording sheet P conveyed by theconveyor belt 5. The recording heads 11C to 11K contain respective fourinks different in color from one another (specifically, a cyan ink, amagenta ink, a yellow ink, and a black ink). As a result of ink ejectionby the recording heads 11C to 11K, a color image is formed on therecording sheet P.

Specifically, the recording heads 11C to 11K sequentially eject therespective inks contained therein to the recording sheet P in the orderof the recording head 11C, the recording head 11M, the recording head11Y, and the recording head 11K. That is, the recording head 11C is thefirst recording head that contains the first ink. The recording head 11Mis the second recording head that contains the second ink. The recordinghead 11Y is the third recording head that contains the third ink. Therecording head 11K is the fourth recording head that contains the fourthink.

Respective relationships of viscosity at 25° C. and pigment contentratio described below are established among the first to fourth inks.The inkjet recording apparatus 100 can prevent offset of an image formedas described above by sequentially ejecting the first to fourth inks inthe relationships.

Viscosity at 25° C.: first ink>second ink>third ink>fourth ink

Pigment content ratio: first ink<second ink≤third ink≤fourth ink

As illustrated in FIG. 2, the recording heads 11C to 11K each are a longrecording head. A longitudinal direction of each recording head 11C to11K is perpendicular to the conveyance direction X of the recordingsheet P. Each of the recording heads 11C to 11K includes a nozzle row N1and a nozzle row N2. Each of the nozzle rows N1 and N2 includes aplurality of nozzles arranged in a direction perpendicular to theconveyance direction X of the recording sheet P. The nozzle rows N1 andN2 are arranged side by side in the conveyance direction X of therecording sheet P. The recording heads 11C to 11K may each be called aline type recording head or long inkjet recording head. A recordingregion of each of the recording heads 11C to 11K is wider than or equalto a width of the conveyed recording sheet P. The nozzles of each of thenozzle rows N1 and N2 are capable of recording one-line image in batcheson the recording sheet P conveyed by the conveyor belt 5.

Note that the inkjet recording apparatus 100 includes the recordingheads 11C to 11K of which the recording regions are each wider than orequal to the width of the recording sheet P. However, the inkjetrecording apparatus according to the present embodiment may for exampleinclude recording head units including a plurality of short recordingheads arranged side by side in series in a width direction of theconveyor belt 5. The short recording heads are arranged such that atotal width of recording regions of the short recording heads is widerthan or equal to the width of the recording sheet P.

The following describes a configuration of an ejection unit 30 includedin each of the recording heads 11C to 11K with reference to FIGS. 3 and4. FIG. 3 is a diagram illustrating the ejection unit 30. FIG. 4 is across-sectional view taken along a line IV-IV in FIG. 3.

As illustrated in FIGS. 3 and 4, the ejection unit 30 includes a nozzle12, an actuator 31, a diaphragm 31 a, a hole 32, a pressure chamber 33,and a nozzle flow channel 34. The hole 32, the pressure chamber 33, thenozzle flow channel 34, and the nozzle 12 communicate with one another.The pressure chamber 33 communicates with a common flow channel 201through the hole 32. A corresponding one of the inks is supplied to thecommon flow channel 201 by for example a non-illustrated pump from anon-illustrated ink tank.

The actuator 31 includes for example a piezoelectric element. Voltageapplication to the piezoelectric element (actuator 31) deforms thepiezoelectric element by inverse piezoelectric effect. Deformation ofthe piezoelectric element is transmitted to the pressure chamber 33through the diaphragm 31 a. As a result, the pressure chamber 33 iscompressed. The ink sent to the pressure chamber 33 from the common flowchannel 201 through the hole 32 is pressurized in the pressure chamber33 by the actuator 31 to be ejected from the nozzle 12 via the nozzleflow channel 34.

FIG. 5 is a block diagram illustrating the configuration of the inkjetrecording apparatus 100. The same reference signs are assigned toelements of configuration common to those in FIGS. 1 and 2, anddescription thereof is omitted. The inkjet recording apparatus 100further includes a controller 20, an interface 21, read-only memory(ROM) 22, random-access memory (RAM) 23, an encoder 24, a motor controlcircuit 25, a recording head control circuit 26, a voltage controlcircuit 27, and a recording medium conveyance motor 28. The interface21, the ROM 22, the RAM 23, the encoder 24, the motor control circuit25, the recording head control circuit 26, and the voltage controlcircuit 27 are connected to the controller 20.

The interface 21 transmits and receives data to and from for example ahost device such as a personal computer. The controller 20 receives animage signal via the interface 21 and performs a scaling process or agrayscale process as necessary to covert the image signal to image data.The controller 20 then outputs a control signal to various controlcircuits which will be described later.

The ROM 22 stores therein for example a control program to drive therecording heads 11C to 11K for image recording. The RAM 23 stores in aspecific region thereof image data after the scaling process or thegrayscale process by the controller 20.

The encoder 24 is connected to the belt drive roller 6. The encoder 24outputs (transmits) a pulse train to the controller 20 according to anamount of rotational displacement of a rotational axis of the belt driveroller 6. The controller 20 calculates an amount of rotation by countingpulses transmitted from the encoder 24 to recognize a feed amount of therecording sheet P (sheet position). The controller 20 outputs thecontrol signal to the motor control circuit 25 and the recording headcontrol circuit 26 based on a signal from the encoder 24.

The motor control circuit 25 drives the recording medium conveyancemotor 28 according to the output signal from the controller 20. Therecording medium conveyance motor 28 drives to rotate the belt driveroller 6.

The recording head control circuit 26 transfers the image data stored inthe RAM 23 to the recording heads 11C to 11K based on the output signalfrom the controller 20. The recording head control circuit 26 controlsink ejection by the recording heads 11C to 11K based on the transferredimage data. Through such ink ejection control on the recording heads 11Cto 11K by the recording head control circuit 26 and control ofconveyance of the recording sheet P by the motor control circuit 25,recording is performed on the recording sheet P.

The voltage control circuit 27 generates an alternating electric fieldby applying voltage to the belt driven roller 7 located on a side wherea sheet is fed from the sheet feed roller 3 based on the output signalfrom the controller 20. The generated alternating electric field causesthe recording sheet P to electrostatically adhere to the conveyor belt5. The electrostatic adhesion is released by grounding the belt drivenroller 7 or the belt drive roller 6 based on the output signal from thecontroller 20. Note that voltage is applied to the belt driven roller 7in the present embodiment. However, voltage may be applied to the beltdrive roller 6.

In the inkjet recording apparatus 100, as illustrated in FIG. 2, the twonozzle rows N1 and N2 of each of the recording heads 11C to 11K arearranged side by side in terms of the conveyance direction X of therecording sheet P (left-right direction in FIG. 2). Ink ejection fromthe nozzles of the two nozzle rows N1 and N2 arranged side by side inthe conveyance direction X forms dots on the recording sheet P conveyedby the conveyor belt 5.

An example of the inkjet recording apparatus according to the presentembodiment has been described so far. However, the inkjet recordingapparatus according to the present embodiment is not limited to theapparatus illustrated in FIGS. 1 to 5.

The inkjet recording apparatus 100 including the four recording heads11C to 11K containing the respective four inks has been described withreference to FIGS. 1 to 5. However, the number of the recording headsincluded in the inkjet recording apparatus according to the presentembodiment is not particularly limited and may be any number larger than2, and may be for example at least 3 and no greater than 10. At least 3and no greater than 5 is preferable.

The inkjet recording apparatus 100 ejects inks in four colors of cyan,magenta, yellow, and black in the stated order, but type and combinationof the inks and order of ejection are not limited to those in the aboveexample. The inkjet recording apparatus according to the presentembodiment may eject for example inks in three colors of magenta,yellow, and cyan in the stated order, eject inks in three colors ofyellow, magenta, and cyan in the stated order, or eject inks in threecolors of cyan, yellow, and magenta in the state order. However, a cyanink typically tends to have a relatively low pigment content ratio inorder to prevent change in hue angle. A magenta ink tends to have arelatively high pigment content ratio in order to ensure sufficientlyhigh color developability. Therefore, in a situation in which the cyanink and the magenta ink are used in the inkjet recording apparatusaccording to the present embodiment, the cyan ink is preferably ejectedearlier than the magenta ink.

The number of nozzles and nozzle intervals of each of the nozzle rows N1and N2 of each recording head 11C to 11K can be set as appropriateaccording to specification of the apparatus.

The two nozzle rows N1 and N2 are arranged side by side in theconveyance direction X in each of the recording heads 11C to 11K.However, 3 or more nozzle rows may be arranged side by side in each ofthe recording heads 11C to 11K in the inkjet recording apparatusaccording to the present embodiment to allow the nozzles of the nozzlerows to sequentially form dot rows. The larger the number of the nozzlerows is, the less frequently defective dots appear in the dot rows.Thus, white lines are hardly perceivable. The inkjet recording apparatusaccording to the present embodiment may be a multifunction peripheralhaving respective functions of a scanner, a copier, a printer, and afacsimile machine.

[Inks]

The following describes the inks used in the inkjet recording apparatusaccording to the present embodiment in detail. Each of the inks containsa pigment. Preferably, the ink may further contain water. The ink mayfurther contain any of a surfactant, a moisturizing agent, a solutionstabilizer, and a penetrating agent.

Each of the inks preferably has a viscosity at 25° C. of at least 3.5mPa·s and no greater than 10.0 mPa·s, and more preferably has aviscosity at 25° C. of at least 3.5 mPa·s and no greater than 7.0 mPa·s.As a result of the inks having a viscosity at 25° C. of at least 3.5mPa·s and no greater than 10.0 mPa·s, ejection stability can beimproved.

Note that a viscosity of the ink is measured using a falling ball typeviscometer. An examples of a falling ball type viscometer that can beused is a falling ball type automatic micro-viscometer (“AMVn”, productof Anton Paar Japan K.K.).

(Pigment)

Examples of pigments include yellow pigments, orange pigments, redpigments, blue pigments, violet pigments, and black pigments. Examplesof yellow pigments include C.I. Pigment Yellow (74, 93, 95, 109, 110,120, 128, 138, 139, 151, 154, 155, 173, 180, 185, or 193). Examples oforange pigments include C.I Pigment Orange (34, 36, 43, 61, 63, or 71).Examples of red pigments include C.I. Pigment Red (122 or 202). Examplesof blue pigments include C.I. Pigment Blue (15, more specifically,15:3). Examples of violet pigments include C.I Pigment Violet (19, 23,or 33). Examples of black pigments include C.I. Pigment Black (7).

Each ink preferably has a pigment content ratio of at least 3.0% by massand no greater than 9.0% by mass. As a result of the pigment contentratio being at least 3.0% by mass, a desired image density can be easilyattained. As a result of the pigment content ratio being no greater than9.0% by mass, fluidity of the pigment in the ink increases, therebyeasily attaining a desired image density. In addition, as a result ofthe pigment content ratio being no greater than 9.0% by mass,permeability of the ink to a recording medium can be improved.

The pigment is dispersed in the ink in the form of particles (alsoreferred to below as pigment particles). The pigment particles mayinclude only the pigment. Alternatively, the pigment particles mayinclude the pigment and resin particles covering the surface of thepigment (also referred to below as covering resin particles).

The covering resin particles cover the surface of the pigment toincrease dispersibility of the pigment. No particular limitations areplaced on a resin contained in the covering resin particles, andexamples of the resin contained in the covering resin particles include(meth)acrylic resins, styrene-(meth)acrylic resins, styrene-maleatecopolymers, vinylnaphthalene-(meth)acrylate copolymers, andvinylnaphthalene-maleate copolymers. (Meth)acrylic resins are resinseach including a repeating unit derived from at least one monomerselected from the group consisting of (meth)acrylate and (meth)acrylateester. Styrene-(meth)acrylic resins are resins each including arepeating unit derived from styrene and a repeating unit derived from atleast one monomer selected from the group consisting of (meth)acrylateand (meth)acrylate ester. Examples of styrene-(meth)acrylic resinsinclude styrene-acrylate-alkyl acrylate ester copolymers,styrene-methacrylate-alkyl methacrylate ester-alkyl acrylate estercopolymers, styrene-acrylate copolymers, styrene-maleate-alkyl acrylateester copolymers, styrene-methacrylate copolymers, and styrene-alkylmethacrylate ester copolymers. As the resin contained in the coveringresin particles, styrene-methacrylate-alkyl methacrylate ester-alkylacrylate ester copolymers and styrene-acrylate copolymers arepreferable, and a styrene-methacrylate-methyl methacrylate-butylacrylate copolymer is more preferable.

The resin contained in the covering resin particles preferably has anacid value of at least 60 mgKOH/g and no greater than 300 mgKOH/g, andmore preferably has an acid value of at least 80 mgKOH/g and no greaterthan 150 mgKOH/g. As a result of the acid value of the resin containedin the covering resin particles being at least 60 mgKOH/g,dispersibility of the pigment particles can be increased. As a result ofthe acid value of the resin contained in the covering resin particlesbeing no greater than 300 mgKOH/g, preservation stability of the ink canbe increased.

In a situation in which the ink contains the covering resin particles,the covering resin particles are preferably contained in the ink in anamount of at least 15 parts by mass and no greater than 100 parts bymass relative to 100 parts by mass of the pigment.

In terms of improving color density, hue, and stability of the ink, thepigment particles preferably have a volume median diameter (D₅₀) of atleast 30 nm and no greater than 200 nm, and more preferably have avolume median diameter (D₅₀) of at least 70 nm and no greater than 130nm.

(Water)

In a case where the ink contains water, the ink preferably containswater in an amount of at least 20% by mass and no greater than 70% bymass.

(Surfactant)

Surfactants improve wettability of an ink to a recording medium.Preferable examples of the surfactants include nonionic surfactants.

Examples of nonionic surfactants that can be preferably used includeacetylene glycol-based surfactants and acrylate polyalkylene glycolalkyl ether-alkyl acrylate-acrylate polyalkylene glycol-laurylacrylate-alkyl methacrylate copolymers. An acetylene glycol-basedsurfactant or an acrylate polyethylene glycol methyl ether-butylacrylate-acrylate polypropylene glycol-lauryl acrylate-methylmethacrylate copolymer is more preferable.

An example of commercially available acetylene glycol-based surfactantsis “OLFINE (registered Japanese trademark) E1010” (product of NissinChemical Industry Co., Ltd.). “OLFINE (registered Japanese trademark)E1010” is a surfactant including an ethylene oxide adduct of acetylenediol.

In a case where the ink contains a surfactant, the surfactant ispreferably contained in the ink in an amount of at least 0.5% by massand no greater than 5.0% by mass in terms of further preventing offsetof a formed image and improving image density.

(Solution Stabilizer)

Solution stabilizers stabilize a solution state of an ink throughimprovement of compatibility of respective components included in theink. Examples of the solution stabilizers include 2-pyrrolidone,N-methyl-2-pyrrolidone, and γ-butyrolactone. In a case where the inkcontains a solution stabilizer, the solution stabilizer is preferablycontained in the ink in an amount of at least 1.0% by mass and nogreater than 20.0% by mass, and more preferably contained therein in anamount of at least 3.0% by mass and no greater than 15.0% by mass.

(Moisturizing Agent)

Moisturizing agents inhibit volatilization of liquid components from anink (particularly, a water-based ink containing water) and stabilizeviscosity of the ink. Examples of the moisturizing agents includepolyalkylene glycol compounds, alkylene glycol compounds, and glycerin.Examples of polyalkylene glycol compounds that can be preferably usedinclude polyethylene glycol and polypropylene glycol. Examples ofalkylene glycol compounds include ethylene glycol, propylene glycol,butylene glycol, diethylene glycol, dipropylene glycol, trimethyleneglycol (1,3-propanediol), triethylene glycol, tripropylene glycol,1,2,6-hexanetriol, thiodiglycol, 1,3-butanediol, 1,5-pentanediol, and3-methyl-1,5-pentanediol. A preferable moisturizing agent is3-methyl-1,5-pentanediol. In a case in which the ink contains amoisturizing agent, the moisturizing agent is contained preferably in anamount of at least 5.0% by mass and no greater than 60.0% by mass.

(Penetrating Agent)

Penetrating agents improve permeability of an ink to a recording medium.Examples of penetrating agents include 1,2-hexylene glycol,1,2-octanediol, 2,4-diethyl-1,5-pentanediol,2-butyl-2-ethyl-1,3-propanediol, triethylene glycol monobutyl ether, anddiethylene glycol monobutyl ether. A preferable penetrating agent istriethylene glycol monobutyl ether or 1,2-octanediol. In a case wherethe ink contains a penetrating agent, the penetrating agent ispreferably contained in the ink in an amount of at least 0.5% by massand no greater than 20.0% by mass, and more preferably contained in theink in an amount of at least 3.0% by mass and no greater than 10.0% bymass.

A plurality of inks are used in the inkjet recording apparatus accordingto the present embodiment. As described above, the inks differ from oneanother in pigment content ratio and viscosity at 25° C.

The pigment content ratio of the first ink is preferably at least 3.0%by mass and no greater than 8.0% by mass, and more preferably at least5.0% by mass and no greater than 7.0% by mass. As a result of thepigment content ratio of the first ink being in the above value range,images having an appropriate density can be formed.

A difference in pigment content ratio between the first ink and thesecond ink is preferably at least 0.5% by mass and no greater than 2.5%by mass, and more preferably at least 0.5% by mass and no greater than1.5% by mass. As a result of the above-mentioned difference being in theabove value range, images having an appropriate density can be formed.

Differences in pigment content ratio between the third to last inks andrespective inks to be precedently ejected (for example, a difference inpigment content ratio between the third ink and the second ink) each arepreferably no greater than 2.5% by mass, and more preferably at least0.5% by mass and no greater than 1.5% by mass. As a result of theabove-mentioned differences being in the above value range, imageshaving an appropriate density can be formed.

The pigment content ratio of the last ink is preferably at least 5.0% bymass and no greater than 9.0% by mass, and more preferably at least 7.0%by mass and no greater than 9.0% by mass. As a result of the pigmentcontent ratio of the last ink being in the above value range, imageshaving an appropriate density can be formed.

The viscosity at 25° C. of the first ink is preferably at least 4.5mPa·s and no greater than 9.0 mPa·s, and more preferably at least 5.0mPa·s and no greater than 7.0 mPa·s. As a result of the viscosity at 25°C. of the first ink being in the above value range, the first ink canhave improved ejection stability and improved permeability to arecording medium.

Differences in viscosity at 25° C. between the second to last inks andrespective inks to be precedently ejected (for example, a difference inviscosity at 25° C. between the second ink and the first ink and adifference in viscosity at 25° C. between the third ink and the secondink) each are preferably at least 0.5 mPa·s and no greater than 3.0mPa·s, and more preferably at least 0.5 mPa·s and no greater than 1.5mPa·s. As a result of the above-mentioned differences being in the abovevalue range, the inks can have improved ejection stability and improvedpermeability to a recording medium.

The viscosity at 25° C. of the last ink is preferably at least 3.5mPa·s, and more preferably at least 3.5 mPa·s and no greater than 5.0mPa·s. As a result of the viscosity at 25° C. of the last ink being inthe above value range, the last ink can have improved ejection stabilityand improved permeability to a recording medium.

No particular limitations are placed on a method for adjusting theviscosity at 25° C. of each ink. An example of the method is changing acontent ratio of a moisturizing agent (for example, an alkylene glycolcompound). Specifically, the viscosity of the ink can be increased byincreasing the content ratio of the moisturizing agent.

Preferably, the inks differ from one another in only one of: type andcontent ratio of the pigment; content ratio of the covering resinparticles; content ratio of the moisturizing agent; and content ratio ofwater. That is, the inks are preferably the same as one another in typeof the covering resin particles, type of the moisturizing agent, andtypes and content ratios of other components (for example, thesurfactant, the penetrating agent, and the solution stabilizer).

(Other Components)

The inks may each contain a known additive (specific examples include ananti-drying agent, an antioxidant, a viscosity modifier, a pH adjuster,and an antifungal agent) as necessary.

[Ink Production Method]

No particular limitations are placed on an ink production method so longas the method enables uniform mixing of a pigment and other componentsblended as necessary. A specific example of the ink production method isa method in which components of an ink are stirred using a stirrer to beuniformly mixed and foreign matter and coarse particles are removed fromthe resultant mixture using a filter (for example, a filter having apore size of no greater than 5 μm).

In a preferable ink production method, a pigment dispersion in whichpigment particles are dispersed in water is prepared by mixing water, apigment, and covering resin particles and a surfactant, which areblended as necessary, and the prepared pigment dispersion is then mixedwith the other component(s). In a case where covering resin particleshaving an acid group are used in ink production, it is preferable toperform equivalent neutralization on the covering resin particles usingan aqueous solution of potassium hydroxide or the like beforepreparation of the pigment dispersion.

In a case where water is added in ink production, ion exchanged water ispreferably added.

The inkjet recording apparatus according to the present embodiment andthe inks used in the inkjet recording apparatus have been described sofar. The inkjet recording apparatus according to the present embodimentcan prevent image offset that may occur through sequential ejection ofthe inks.

Second Embodiment: Inkjet Recording Method

An inkjet recording method according to the present embodiment includessequentially ejecting three or more different inks onto a recordingmedium. Each of the different inks contain a pigment. Of the differentinks, an ink to be ejected first has the lowest pigment content ratio.Of the different inks, an ink to be ejected third and an ink to besubsequently ejected each have a pigment content ratio equal to orhigher than a pigment content ratio of a corresponding one of inks to beprecedently ejected. Of the different inks, the ink to be ejected secondand an ink to be subsequently ejected each have a lower viscosity at 25°C. than a corresponding one of inks to be precedently ejected.

The inks used in the inkjet recording method according to the presentembodiment may be the same as the inks used in the inkjet recordingapparatus according to the first embodiment. The inkjet recording methodaccording to the present embodiment can be implemented for examplethrough use of the inkjet recording apparatus according to the firstembodiment. The inkjet recording method according to the presentembodiment can prevent image offset that may occur through sequentialejection of the inks.

EXAMPLES

The following describes examples of the present disclosure. However, thepresent disclosure is in no way limited to the following examples.

(Preparation of Pigment Dispersion C)

A 0.6-L vessel was charged with a cyan pigment (“LIONOL (registeredJapanese trademark) BLUE FG-7330”, product of TOYOCOLOR CO., LTD.,component: copper phthalocyanine, color index: Pigment Blue 15:3),later-described covering resin particles A, a surfactant (“OLFINE(registered Japanese trademark) E1010”, product of Nissin ChemicalIndustry Co., Ltd), and ion exchanged water at a ratio shown in Table 1below. Subsequently, the vessel contents were mixed using a media typewet disperser (“DYNO (registered Japanese trademark)-MILL”, product ofWilly A. Bachofen AG (WAB)).

TABLE 1 Content ratio [% by mass] Covering resin particles A 6.0 Cyanpigment 15.0 Surfactant 0.5 Water Remainder Total 100.0

The covering resin particles A used were resin particles (volume mediandiameter (D₅₀): 100 nm) constituted by an alkaline-soluble methacrylicacid (MAA)-methyl methacrylate (MMA)-butyl acrylate (BA)-styrene (ST)copolymer (mass average molecular weight (Mw): 20,000, acid value: 100mgKOH/g). The covering resin particles A were anionic. A mass ratio of arepeating unit derived from MAA, a repeating unit derived from MMA, arepeating unit derived from BA, and a repeating unit derived from ST(MAA unit/MMA unit/BA unit/ST unit) was 40/15/30/15 in the resinconstituting the covering resin particles A.

Each mass average molecular weight (Mw) of the covering resin particlesA and a later-described nonionic surfactant was measured by a gelpermeation chromatography (“HLC-8020GPC”, product of Tosoh Corporation)under the following conditions. In the measurement, a calibration curvewas plotted using n-propylbenzene and F-40, F-20, F-4, F-1, A-5000,A-2500, and A-1000, which are TSKgel standard polystyrenes produced byTosoh Corporation.

(Conditions for Measuring Mass Average Molecular Weight)

Column: “TSKgel SuperMultipore HZ-H” (product of Tosoh Corporation,semi-micro column having an internal diameter of 4.6 mm and a length of15 cm)

-   -   Number of columns: 3    -   Eluent: Tetrahydrofuran    -   Flow rate: 0.35 mL/minute    -   Sample injection amount: 10 μL    -   Measurement temperature: 40° C.    -   Detector: Infrared (IR) detector

Note that the covering resin particles A were subjected to equivalentneutralization with an aqueous KOH solution of 105% by mass and thenused for preparation of the pigment dispersion C. An amount of KOH addedwas calculated based on the mass of the copolymer that was aneutralization target. Note that “Water” in Table 1 includes watergenerated in reaction for neutralizing the covering resin particles Aand water included in the aqueous KOH solution used for neutralizationof the covering resin particles A in addition to ion exchanged watercharged into the vessel.

Subsequently, a medium (zirconia beads having a particle diameter of 0.5mm) was charged into the vessel to adjust a dispersion state so that thepigment particles had a desired volume median diameter (D₅₀).Specifically, the medium (zirconia beads) in an amount of 70% by massrelative to the capacity of the vessel was charged into the vessel, andwas dispersed into the vessel contents under conditions of a temperatureof 10° C. and a peripheral speed of 8 m/second while the vessel contentswere cooled with water. Through the above, a pigment dispersion C wasobtained that included pigment particles having a volume median diameter(D₅₀) of 100 nm (pigment particles of the cyan pigment covered with thecovering resin particles A).

As for the volume median diameter (D₅₀) of the pigment particles, mediandiameters (D₅₀) of measurement samples were measured using a dynamiclight scattering type particle size distribution analyzer (“ZERASIZERNANO ZS”, product of Sysmex Corporation). The measurement samples eachwere a solution obtained by diluting the pigment dispersion C with ionexchanged water by 300 times. In the measurement, 10 measurement sampleswere prepared and each volume median diameter (D₅₀) of the 10measurement samples was measured. An arithmetic mean value of themeasured ten measurement values was taken to be a volume median diameter(D₅₀) of the pigment particles.

(Preparation of Pigment Dispersion Y and Pigment Dispersion M)

A pigment dispersion Y and a pigment dispersion M were preparedaccording to the same method as for the pigment dispersion C in allaspects other than the following changes. While the cyan pigment wasused in preparation of the pigment dispersion C, a yellow pigment(“FY840 (Fast Yellow 74)”, product of Dainichiseika Color & ChemicalsMfg. Co., Ltd., component:2-[(2-methoxy-4-nitrophenyl)azo]-N-(2-methoxyphenyl)-3-oxobutanamide,color index: Pigment Yellow 74) was used in preparation of the pigmentdispersion Y and a magenta pigment (“FASTOGENSUPER MAGENTA R”, productof Dainichiseika Color & Chemicals Mfg. Co., Ltd., comment:2,9-dimethylquinacridone, color index: Pigment Red 122) was used inpreparation of the pigment dispersion M.

[Preparation of Inks]

With respect to each of the inks, components of types and content ratiosshown in Tables 2 and 3 below were loaded into a stirrer (“THREE-ONEMOTOR BL-600”, product of Shinto Scientific Co., Ltd.) and stirred at arotational speed of 400 rpm for uniform mixing. The above-describedpigment dispersions C, M, and Y were used as pigment dispersions inTables 2 and 3 below. In order to remove foreign matter and coarseparticles from the resultant mixture, the resultant mixture was filteredusing a filter having a pore size of 5 μm. Through the above, magentainks (M-1) to (M-5), yellow inks (Y-1) to (Y-5), and cyan inks (C-1) to(C-6) were obtained.

TABLE 2 % by mass Pigment dispersions See Table 33-Methyl-1,5-pentanediol See Table 3 2-Pyrrolidone 7.0 Nonionicsurfactant 2.5 Triethylene glycol monobutyl ether 5.0 1,2-Octanediol 0.5Ion exchanged water Remainder Total 100.0 

The nonionic surfactant shown in Table 2 was a polyethylene glycolmethyl ether acrylate (PEGA)-butyl acrylate (BA)-polypropylene glycolacrylate (PPGA)-lauryl acrylate (LA)-methyl methacrylate (MMA)copolymer. In the copolymer, a mass ratio of a repeating unit derivedfrom PEGA, a repeating unit derived from BA, a repeating unit derivedfrom PPGA, a repeating unit derived from LA, and a repeating unitderived from MMA (PEGA unit/BA unit/PPGA unit/LA unit/MMA unit) was60/10/10/12/8. The nonionic surfactant had a surface tension of 30.5mN/m and a mass average molecular weight (Mw) of 5,000. The nonionicsurfactant was water soluble. Note that the surface tension of thenonionic surfactant was measured by the Wilhelmy method using a surfacetensiometer (“CBVP-Z”, product of Kyowa Interface Science Co., Ltd.) ata liquid temperature of 25° C.

The viscosity at 25° C. of each ink was measured using a falling balltype automatic micro viscometer (“AMVn”, product of Anton Paar JapanK.K.). The viscosity measurement was carried out using a capillaryhaving a diameter of 1.6 mm and a steel ball having a diameter of 1.5 mmand a specific gravity of 7.63 under conditions of a falling ball angleof 70 degrees and a temperature of 25° C. After the measurement, theviscosity of the ink was calculated using dedicated software to “AMVn”(product of Anton Paar Japan K.K.) above.

<Evaluation>

[Preparation of Evaluation Apparatuses]

Evaluation apparatuses used each were an inkjet recording apparatushaving the configuration of the inkjet recording apparatus 100 in FIG. 1(a prototype evaluation apparatus produced by KYOCERA Document SolutionsInc.). However, inks contained in respective four recording heads andlocation of nozzles in each recording head were changed from those inFIG. 1 as appropriate. With respect to each of the evaluationapparatuses, one of the magenta inks (M-1) to (M-5), one of the yellowinks (Y-1) to (Y-5), and one of the cyan inks (C-1) to (C-6) were loadedinto respective three recording heads of the four recording heads. Typesand order of ejection of the inks used are shown in Table 3 below.

In Table 3 below, the term “MPD” represents a content ratio of3-methyl-1,5-pentanediol in each ink. The term “Viscosity” represents aviscosity of an ink at 25° C. Note that the viscosity at 25° C. of eachink used in Examples was predominantly determined according to type andcontent ratio of the pigment and the content ratio of3-methyl-1,5-pentanediol. For the reason as above, the viscosity at 25°C. of the ink and the content ratio of 3-methyl-1,5-pentanediol are notnecessarily in proportion to each other.

TABLE 3 Pigment dispersion MPD Pigment [% by [% by [% by Viscosity InkType mass] mass] mass] [mPa · s] Example 1 First ink M-1 Magenta 40.0 156.0 6.0 Second ink Y-1 Yellow 46.7 12 7.0 5.0 Third ink C-1 Cyan 53.3 108.0 4.0 Example 2 First ink Y-2 Yellow 26.7 22 4.0 8.0 Second ink M-1Magenta 40.0 15 6.0 6.0 Third ink C-2 Cyan 53.3 10 8.0 4.5 Example 3First ink C-3 Cyan 26.7 18 4.0 8.0 Second ink Y-3 Yellow 40.0 16 6.0 7.0Third ink M-2 Magenta 40.0 18 6.0 4.5 Comparative First ink C-4 Cyan40.0 16 6.0 8.0 Example 1 Second ink Y-4 Yellow 66.7 12 10.0 6.0 Thirdink M-3 Magenta 26.7 20 4.0 4.5 Comparative First ink C-5 Cyan 66.7 1210.0 6.0 Example 2 Second ink Y-5 Yellow 40.0 15 6.0 6.0 Third ink M-4Magenta 26.7 22 4.0 5.0 Comparative First ink M-5 Magenta 66.7 12 10.04.0 Example 3 Second ink Y-5 Yellow 40.0 17 6.0 6.0 Third ink C-6 Cyan26.7 19 4.0 7.0

The following describes the recording heads of each evaluation apparatusin detail. Each of the recording heads included the ejection units 30illustrated in FIGS. 3 and 4. In each of the ejection unit 30, thepressure chamber 33 had a sectional area of 0.2 mm², a width of 200 μm,and a depth of 100 μm. The nozzle flow channel 34 had a diameter of 200μm and a length of 800 μm. The hole 32 had a diameter of 30 μm and alength of 40 μm. The nozzle 12 had a length of 30 μm. The nozzle 12 hadan opening in a circular shape with a radius of 10 μm. On a substrate ofthe recording head, four nozzle rows are arranged and 166 nozzles 12were arranged in each of the four nozzle rows (664 nozzles 12 in total).In each nozzle row of the nozzles 12, the nozzles 12 were arranged at apitch of 150 dpi. Adjacent nozzle rows of the recording head werestaggered in a direction along the rows by ¼ of the pitch to attain 600dpi as a whole.

[Image Printing]

Solid images each having a size of 10 cm by 10 cm were printed on sheetsof A4-size plain paper (“PDW”, product of MITSUBISHI PAPER MILLSLIMITED) using the respective evaluation apparatuses in anormal-temperature and normal-humidity environment at a temperature of25° C. and a relative humidity of 60%. In the image printing, the yellowink, the magenta ink, the cyan ink each in an amount of 3.6 pL (11 pL intotal) were ejected from the respective recording heads to print atertiary color image.

[Image Density Measurement]

With respect to each sheet of the paper with the solid image printedthereon, a surface of the sheet with the solid image printed thereon wasrubbed with non-printed paper 10 times in a reciprocal manner whileapplying a load of 1 kg. Thereafter, whether or not stain was made onthe surface of the sheet of paper with the solid image printed thereonthrough the non-printed paper rubbing. Measurement was carried out in amanner that a reflection density of a non-printed portion of the sheetof the paper where the solid image has not been printed (a region 1 cmapart from an edge of the solid image) was measured using a reflectancedensitometer (“RD-19”, product of X-Rite Inc.). A lower image density ofthe non-printed portion indicates that image offset could be moreprevented. If the image density of the non-printed portion is less than0.020, evaluation as being able to prevent image offset can be made. Ifthe image density of the non-printed portion is at least 0.020,evaluation as not being able to prevent image offset can be made.Measurement results are shown in Table 4 below.

TABLE 4 Comparative Comparative Comparative Example 1 Example 2 Example3 Example 1 Example 2 Example 3 Offset prevention 0.002 0.005 0.0060.027 0.025 0.030

The evaluation apparatuses of Examples 1 to 3 each included three ormore recording heads. The recording heads contained different inks andejected the different inks sequentially on a recording medium. Thedifferent inks each contained a pigment. Of the different inks, an inkto be ejected first had the lowest pigment content ratio. Of thedifferent inks, an ink to be ejected third and an ink to be subsequentlyejected (specifically, the third ink) each have a pigment content ratioequal to or higher than that of the pigment contained in a correspondingone of inks to be precedently ejected (specifically, the second ink). Ofthe different inks, an ink to be ejected second and an ink to besubsequently ejected (specifically, the second ink and the third ink)each had a lower viscosity at 25° C. than a corresponding one of inks tobe precedently ejected (specifically, the first ink and the second ink).As a result, each of the evaluation apparatuses of Examples 1 to 3 couldprevent offset of a formed image.

By contrast, the evaluation apparatuses of Comparative Examples 1 to 3did not meet the above conditions. Specifically, the pigment contentratio of the third ink was lower than the pigment content ratio of thesecond ink in the evaluation apparatus of Comparative Example 1. In theevaluation apparatus of Comparative Example 2, the pigment content ratioof the first ink was the highest of the first to third inks. In also theevaluation apparatus of Comparative Example 2, the third ink had a lowerpigment content ratio than the second ink. In the evaluation apparatusof Comparative Example 2, the second ink and the first ink had the sameviscosity at 25° C. as each other. In the evaluation apparatus ofComparative Example 3, the pigment content ratio of the first ink wasthe highest of the first to third inks. In also the evaluation apparatusof Comparative Example 3, the third ink had a lower pigment contentratio than the second ink. In the evaluation apparatus of ComparativeExample 3, the second ink had a higher viscosity at 25° C. than thefirst ink and the third ink had a higher viscosity at 25° C. than thesecond ink. As a result, each of the evaluation apparatuses ofComparative Examples 1 to 3 could not prevent offset of a formed image.

From the above results, offset of a formed image can be thought to beprevented according to the present disclosure.

What is claimed is:
 1. An inkjet recording apparatus comprising three ormore recording heads, wherein the recording heads contain different inksand eject the different inks sequentially on a recording medium, thedifferent inks each contain a pigment, of the different inks, an ink tobe ejected first has a lowest pigment content ratio, of the differentinks, an ink to be ejected third and an ink to be subsequently ejectedeach have a pigment content ratio equal to or higher than that of thepigment contained in a corresponding one of inks to be precedentlyejected, and of the different inks, an ink to be ejected second and anink to be subsequently ejected each have a lower viscosity at 25° C.than a corresponding one of inks to be precedently ejected.
 2. Theinkjet recording apparatus according to claim 1, wherein differences inthe viscosity at 25° C. of the ink to be ejected second and the ink tobe subsequently ejected from respective inks to be precedently ejectedeach are at least 0.5 mPa·s and no greater than 3.0 mPa·s.
 3. The inkjetrecording apparatus according to claim 1, wherein of the different inks,an ink to be ejected last has a viscosity at 25° C. of at least 3.5mPa·s.
 4. The inkjet recording apparatus according to claim 1, wherein adifference in the pigment content ratio between the ink to be ejectedfirst and the ink to be ejected second among the different inks is atleast 0.5% by mass and no greater than 2.5% by mass.
 5. The inkjetrecording apparatus according to claim 1, wherein differences in thepigment content ratio of the ink to be ejected third and the ink to besubsequently ejected from respective inks to be precedently ejectedamong the different inks each are no greater than 2.5% by mass.